My son was born in a military hospital. He was issued a Department of State ConsularReport of Birth Abroad of a and is a US citizen and citizen of North Carolina.
The part about US Soil is that every flag pole is sunk in soil from the United States, symbolizing our sovereignty at that post; you are correct that it is not US Soil for citizenship....
Or, like McCain, off the US military base in a civilian hospital? - McCain was derived from his parent being in the military, for which their are stipulations in law to address concerning citizenship, separate but overlapping the similar stipulations for "born of two US citizen parents".
A Consular Report of Birth Abroad may be issued for any U.S. citizen child under the age of 18 who was born abroad and who acquired U.S. citizenship at birth. Only the child's parent(s), legal guardian, person acting in loco parent is or the child may apply on the child's behalf. The application generally must be signed before a U.S. consular officer, a consular agent, or, in the case of children born in U.S. military hospitals, a designated military official. A Consular Report of Birth Abroad is proof of U.S. citizenship; however, and does not take the place of a passport for travel purposes.
The UCMJ ALLOWS for individual states and the Federal government to enforce their laws but the UCMJ can legally enforce much stricter laws since many federal laws do not apply to service men.
I believe that the UMCJ can even allow foreign governments to enforce some of their laws on service men stationed in those countries in the matter of civilian law and not military law.